The principle goal of this project is to define the cellular states and signals that control the cell types and synapses in the central nervous system. The work in this program is based on the identification of stem cells in the nervous system. These cells can be obtained from the developing and adult nervous system and they can generate the differentiated cells of the nervous system, neurons, astrocytes and oligodendrocytes. In the past year, in these studies on the fundamental biology of nervous system stem cells we have: 1. designed and built a high resolution imaging system to define the lineage and responses of stem cells differentiating into neurons, astrocytes and oligodendrocytes. This imaging system was built here and is the only one in the world that allows stable long term culture of differentiating cells. Using this system we show that stem cells generate the major cell types in the brain within a 24 hour period. Any studies of the mechanisms of fate choice must target the events that occur in this restricted time window. 2. identified fundamental cell growth pathways downstream of the Notch receptor that promote embryonic, fetal and adult stem cell expansion in vitro. Stem cell therapies are limited because it is difficult to control their growth. Our work demonstrates that the Notch receptor activates the PI3kinase/Akt signaling pathway, identifies a serine site on STAT3 as an integrator of survival signaling initiated by insulin, gp130 and Notch receptors and shows that enhanced endogenous adult stem cell growth correlates with behavioral improvement following brain injury. 3. shown that the sonic hedgehog (shh) expressing medial floor-plate cells of the midbrain are the immediate precursors to dopamine neurons. This work is the first to map the neuronal precursor domains of the ventral midbrain and to show that dopamine neurons are derived from floor-plate cells. The identification of dopamine precursors as floor plate cells will have a direct influence on methods to derive dopamine neurons from precursors found in the fetal and adult precursors. 4. developed a cell culture system to identify the molecular mechanisms controlling the activity dependent survival of hippocampal neurons. The construction of the CNS occurs in several distinct developmental steps. Following neural proliferation, cells that have left the cell cycle generally migrate to their final locations. Many cell types, neurons included, undergo a form of developmental cell death following migration. For neurons, this generally occurs at the time of neuron-target contact and initial synaptogenesis. We have investigated a form of endogenously occurring cell death in vitro that occurs at the time of synapse formation suggesting that this may be an ideal model system to better understand the mechanisms of neuronal survival and death.